The extensive use of semiconductors, such as integrated circuit ("IC") devices, in a wide range of electronic applications is well known. A typical semiconductor device is comprised of a series of contact openings ("windows") formed in a substrate material, such as silicon that has doped source and drain regions. The interconnection of these windows provides a circuit for the conduction of electrical current through the device. The windows have a metallic "plug" deposited therein, which is tungsten in most applications. The plug is overlaid with a conductive metal trace, such as aluminum-alloy, which includes, for example, aluminum-copper, aluminum-silicon or aluminum-copper-silicon. The conductive metal trace is laid down in a predetermined pattern that electrically connects the various windows to achieve the desired electrical circuit configuration within the semiconductor device.
Typically, the windows have a barrier layer of titanium overlaid with titanium nitride formed over the surface of the interior sides of the window to serve as an adhesion/nucleation layer for tungsten. Various problems, however, have arisen with respect to the metals used to form the plugs and trace patterns between these windows. For example, the titanium and titanium nitride layers are typically deposited by physical vapor deposition ("PVD"), whereas the tungsten is deposited by chemical vapor deposition ("CVD"). These different deposition methods use very different tools to achieve the deposition. Thus, the semiconductor device is placed in a PVD tool for the formation of the titanium and titanium nitride layers, removed and placed in a CVD tool to form the tungsten plug, and then returned to the PVD tool for the deposition of the aluminum-alloy interconnect. These transfers not only require time, it also subjects the device to oxidation and contaminants, which in turn, can affect the quality of the device. Moreover, because tungsten does not have a sufficiently high enough electrical conductivity, the excess tungsten that is deposited on the surface of the semiconductor device must be etched-back or polished-back prior to its return to the PVD tool, which involves yet another step in the manufacturing process. These inefficiencies increase the overall manufacturing time and cost of the semiconductor device.
In view of these disadvantages, it has become desirable to use aluminum-alloys for the metal plug. Unfortunately, however, aluminum-alloy also has problems associated with its use. It is well known that mutual diffusion of aluminum-alloy and silicon occurs between the silicon substrate and the aluminum-alloy plug when the semiconductor device is subjected to the high temperatures necessary for semiconductor manufacturing. The aluminum-alloy can diffuse into the silicon substrate to such a depth to cause a short within the semiconductor device. This phenomenon is known as junction leakage. The aluminum-alloy is able to diffuse into the silicon substrate because conventional processes produce barrier layers that have crystalline structures with grain boundaries. As such, the aluminum-alloy is capable of diffusing through these grain boundaries and into the silicon substrate.
Attempts have been made to address the problem of the diffusion problem associated with such crystalline structures. Two such attempts are disclosed in U.S. Pat. No. 4,976,839 and U.S. Pat. No. 5,514,908. Both of these patents are directed to processes that are designed to circumvent the problems associated with such crystalline structures and resulting grain boundaries existing within the barrier layers. However, they too fall short in providing a satisfactory solution in that they may form grain boundaries that might not be adequately stuffed with oxygen as a result of the complex manufacturing processes to achieve a layer boundary through which aluminum-alloy will not diffuse.
Therefore, what is need in the art is a semiconductor and a simple process for manufacturing thereof that avoids the problems associated with crystalline barrier layers that allow diffusion of the aluminum into the silicon. The semiconductor and the manufacturing process of the present invention address these needs.